In an image forming device, e.g. digital copying machine, optical printer, etc., with optical scanning and recording in a conventional electrophotographic system, used is an optical scanning arrangement in which an image carrier such as a photoconductor drum and an optical scanning unit such as an LSU (Laser Scanning Unit) and an LED (Light Emitting Diode) line head are positioned mutually in a predetermined positional relation in a frame of a main body. Also, with optical beams modulated in accordance with image data in the optical scanning unit, the image carrier surface is scanned and exposed so that images are recorded and reproduced.
In such an optical scanning arrangement, a positional relation between the image carrier and the optical scanning unit affects image quality of images to be recorded and reproduced.
Consequently, in order to adjust the mutual positional relation between the image carrier and the optical scanning unit, adopted are a method of adjusting a position for installing the optical scanning unit itself or a method of adjusting a reflection mirror positioned just in front of a scanning target such as the photoconductor drum.
Further, in case of a plurality of scanning beams, adjustment in the positional relation between the scanning target and the optical scanning unit can be arranged by a method of mounting the optical scanning unit in a case including the scanning target after adjusting a position for mounting the optical scanning unit so that the plurality of scanning beams run in parallel. Alternatively, adjustment for each optical scanning unit can be arranged in installing each optical scanning unit in the case.
The above methods have been devised to adjust a deviation of the positional relation between the scanning target and the optical scanning unit for the purpose of obtaining an excellent image quality.
Incidentally, as to a color image forming device, a so-called image forming device in tandem system, utilizing a plurality of image carries and optical scanning units having the number corresponding to the number of the image carriers, has been developed in recent years in order to increase a speed of color image formation. In the image forming device in tandem system (hereinafter referred to as “tandem apparatus”), optical scanning units have been arranged separately, and adjustment in mutual positions between the image carriers and the optical scanning units has been carried out by a method of adjusting a position for mounting the optical scanning unit.
However, in the conventional optical scanning arrangement, the optical scanning units are adjusted by each unit, resulting in a subtle deviation occurred between the optical scanning units and the scanning target after installing them in a main apparatus. Although this deviation can be adjusted by adjustment in the position of the reflection mirror as described above, it is necessary to move the reflection mirror and its supporting member together. Therefore, it is necessary to adjust the position of the mirror not only in a wide area but also in multi-directions. Because of this, there is a problem of difficulty in fine adjustment.
Further, in case of the tandem apparatus which has the plurality of optical scanning units, there has been a problem of a high cost. Therefore, considered has been an optical scanning arrangement in a system in which optical deflecting means for scanning with beam are shared, and a single optical deflecting means scan with a plurality of scanning beams.
Thus, in the optical scanning arrangement in such a system that the single optical deflecting means scans with the plurality of scanning beams, an optical scanning unit has one-unit-structure. Therefore, in the previous method of adjusting the positions for mounting the optical scanning units for positional deviations of the image carriers, it is impossible to perform the positional adjustment of each optical scanning line corresponding to each image carrier. More specifically, only a method of adjusting the position of the mirror disposed in a light path between the optical deflecting means and each image carrier can adjust the positional deviation.
Therefore, in order to adjust the positional deviation which occurs after the optical scanning arrangement has been installed to the main apparatus, the movement of the mirror position is required. Also, in the method of adjusting by moving the mirror position, desired are the movement of the mirror position only in a certain direction and a small influence on images with the movement of the mirror position; especially, the influence on scanning properties is desired as small as possible.